Technologies for material synthesis without using materials having a high environmental burden such as organic solvents have been necessary in recent years. Ultrafine processes such as in integrated circuit manufacturing have been commonly performed using dry processes (vacuum processes) such as in a vacuum, a rarefied gas atmosphere, or a plasma discharge atmosphere.
The dry processes have been developed as highly effective means in terms of the advantage of ability to directly use atoms/molecules or ions in the processes. However, the needs such as for a facility to maintain vacuum and a plasma generator are high-cost factors. On the other hand, wet processes using a liquid such as for plating and cleaning results in producing an enormous amount of wastewater, which may cause an environmental problem.
A supercritical CO2 fluid with has unique properties, such as having an intermediate quality between liquid and solid, having zero surface tension, and having a high ability to dissolve other substances (dissolvability). Furthermore, a supercritical fluid has advantages, such as chemically stable, low price, harmless and low cost. In addition to them, a supercritical fluid has many features, such as that CO2 itself and substances dissolved in CO2 fluid are recyclable by vaporization and reliquefaction.
Research and development using supercritical CO2 have been advanced centering on a wafer cleaning process in integrated circuit manufacturing processes. For example, in a cleaning process, a process focusing on the dissolvability, safety and recyclability of supercritical CO2 has been developed. Also, in supercritical CO2, focusing on the zero surface tension, research and development of ultrafine process for nanoscale wiring have been conducted.
For example, a thin film formation is one of the main functions in the manufacture of semiconductor equipment, and Rapid Expansion of Supercritical Solution is known as a method for thin film formation using a supercritical fluid. D. Matson and the collaborators disclosed a technology for forming a supersaturated material by expanding a supercritical fluid in which source materials dissolve. And a further developed technology has been also disclosed, which is a method for obtaining a metal oxide thin film by dissolving oxide complexes in a supercritical fluid and spraying it on a heated substrate (See patent document 1 and non-patent document 1).
A supercritical fluid penetrates extremely deeply into a nanopore since the surface tension is zero and the diffusion coefficient is large. If a supercritical fluid itself can be used as a reaction medium for thin film formation, it will become possible to form and fill a substance in an ultrafine structure, and further to develop a low-cost green process replacing CVD and plating.
The inventors have developed independently a method for forming a thin film by dissolving thin film forming materials such as an organic metal in supercritical CO2 and then letting a deposition reaction proceed (E. Kondoh and H. Kato, Microelectron. Eng. Volume 64 (2002), Page 495), and have applied the method to the manufacture of integrated circuit wires, such as Cu filling into viaholes and trenches and forming diffusion prevention films (Japanese Patent Application No. 2003-17948 “handotaisochi no seizohoho” (Method of manufacturing semiconductor apparatus), Japanese Patent Application No. 2003-17949 “handotaisochi no seizohoho” (Method of manufacturing semiconductor apparatus)). Also, the same sort of method has been disclosed in Published Japanese translation of PCT application No. 2003-514115.
Patent document 1: Japanese Patent Application Publication No. 2003-213425
Non-patent document 1: J. Mater. Sci. Volume 22, Issue 6, 1918 (1987)
Patent document 2: Japanese Patent Application No. 2003-17949
Patent document 3: Japanese Patent Application Publication No. 2003-514115